Bob,
Oil thermostats have 4 fittings like this:
because they have the bypass built in. So you should never have a restriction or see a drop in
oil pressure. I've plumbed them before with -10 fittings and I realize it's a pain any time you've got to redo
oil lines, but it's not that big of a deal. I think it's well worth it since the engine oil will reach decent operating temps.
Mike